The present invention relates to line card shelves, and more particularly to line card shelves for use with spectrally incompatible signal groups.
Copper wire pairs are used to provision many telephony services. The copper pairs, also referred to as a loop, typically extend from a customer's premises and terminate at a main distribution frame (MDF) in a telephone company central office. The copper pairs are arranged in bundles, typically of twenty-five or more pairs. These bundles are referred to as outside plant cable.
Outside plant cable is connected to an inside cable through a protection device at the main distribution frame. The protection device isolates central office equipment from external hazards such as electrical surges due to lightning strikes on the external cable. Inside cable, typically arranged like outside cable in bundles that consist of fifty wires arranged in two-wire pairs, is used to connect to a central office line card shelf. The line card shelf is a terminating point for the copper loop between the central office and the customer's location.
At the line card shelf, inside plant cable is terminated on conductive terminals. These terminals provide signal paths to line card receptacle connectors in the line card shelf. A circuit board, known as a line card, is inserted in a shelf receptacle connector forming a signal path between line card circuitry and the copper loop. Line cards and associated line card shelf circuitry are used to transmit signals on copper loops and to link copper loops to central office switching equipment. The line card shelf provides a link to central office switching equipment through master shelf interface circuitry.
Signals transmitted to and from the line card shelf on copper pairs are subject to interference caused by electromagnetic fields. Interfering fields are produced by, for example, signals carried on other copper loops. When copper loops are in close proximity, such as when they are located next to each other in an inside cable or in an outside cable, the electromagnetic fields produced by one copper pair may induce interference signals on other pairs. These interference signals are problematic for some transmission technologies. To minimize interference in such technologies, wire pairs must be carefully separated to minimize coupling of spectrally incompatible signals.